The Internet, as it has grown considerably in size and popularity, is being used to provide various services and applications to users. Diverse applications, such as streaming a short movie demonstrating how to assemble a piece of furniture, taking a virtual tour of a real estate property or a scenic spot, watching a live performance of an artist, and participating in a networked multi-user computer game or conference, are all available to users via the Internet.
An important trend is that users are no longer satisfied with receiving services that are targeted at mass audiences. Users are demanding services that are tailored to their individual needs. For example, a user may desire to receive content in a particular language, or a user may require a transcoded-down version of a movie to view on a personal digital assistant (PDA). With the proliferation of personalized services, an important challenge facing future network infrastructure is balancing the tradeoffs between providing individualized services to each user and making efficient use of network resources. Due to high bandwidth requirements and intensive computations incurred by multimedia applications, traditional unicast delivery of services may not be able to meet the transmission requirements of individualized services and is not scalable to efficiently meet the demands of a large number of service providers and users.
Network layer multicasting, also known as IP multicasting, is more scalable and more efficient than unicast delivery of services. However, IP multicasting is not widely supported in the Internet infrastructure and is not widely used in private networks. In addition, services, such as multimedia applications, typically have stringent delivery requirements for maintaining the perceptual quality of the delivered multimedia as seen by a user. Traditional IP multicast trees may not support a level of end-to-end quality of service (QoS), which may be needed for the delivery of certain services. In addition, tree reconfiguration, which is performed periodically in conventional IP multicasting for network maintenance, may cause further degradation of the quality of delivered services.